Process of separating aqueous and other vapors from fluids and solids and for preparing dilute sulphuric acid



O. MAASS..

PROCESS OF SEPARATING AQUEOUS AND OTHER VAPORS FROM FLUIDS AND SOLIDS AND FOR PREPARING DILUTE SULPHURIC ACID.

APPLICATION FILED APR115, 1918- I 1,417,618. Patented May 30,1922.

G T SUCTION .5)! I 1 M27 a ()FFICE."

OTTO MAASS, OF MONTREAL, QUEBEC, CANADA.

PROCESS OF SEPARATING AQUEOUS AND OTHER VAPOR-S FROM FLUIDS, AND

AND FOR PREPARING- DILUTE SULPI-IUBIC ACID.

seems Specification of Letters Patent. Patented lvlay 30,

Application filed April 15, 1918. Serial No. 228,733.

' T 0. all ham it may concern Be it known that I, OTTO MAASS, a subject of the King of Great Britain, and resident of the city of Montreal, in the Province of Quebec and Dominion of Canada, have invented certain new and useful Improvements in Processes of Separating A ueous and Other Vapors from Fluids and olids and for Preparing Dilute Sulphuric Acid, of which the following is a full, clear, and exact description.

This invention relates to a process or method of separating aqueous or other vapors from gases, liquids or solids, and the object of the invention is to provide for the very rapid extraction of the vapors under such conditions that the substance cleansed of the vapor is not affected.

At the present time, it is customary to dry gases by passing them through sulphuric acid, the aqueous moisture being absorb'ed by the acid. This method is quite satisfactory as a laboratory operation but for commercial use it is entirely too slow in the majority of cases. When it is desired to remove aqueous vapor from liquids or solids, a process of evaporation is resorted to, in which the rapidity of evaporation can be increased by raising the temperature of the material or lowering the atmospheric pressure. In many instances, it is not practicable to raise the temperature to any considerable degree above normal atmospheric temperatures, as the substance which it is desired to evaporate is injured or changed at the higher temperatures. In the same manner, the process of freezing out aqueous moisture cannot be always resorted to. In any event, the ordinary processes of evaporation at either high or low temperatures are tedious and expensive, and therefore unsuitable for many commercial uses.

According to this invention, abstraction of aqueous or other moisture from gases, liquids or solids may be carried on with great rapidity and at low cost, at temperatures which do not affect the material being dried. For example, chemical substances such as hydrogen peroxide, which normally exist as weak aqueous solutions, may. be quickly and cheaply concentrated at temperatures which will not decompose or change the substance. From an ordinary commercial aspect, the invention is equally useful. For example, milk may be evap'orated to a dry powder in a veryshort time and at low cost, and without raising the,

temperature of the milk anywherenear the point which would cause undesirable changes in it. Sulphuric acid is preferably used as the drying medium, where aqueous moisture is to be removed, and the materlal .to be dried and the acid are confinedin a closqgl,

apparatus at sub-atmospheric pressure. pecullarlty of this inventionis that the sulphuric acid is used to create a vacuum in the apparatus.

In the accompanying diagram which illustrates the invention ;11 designatesa receptacle containing the material to be dried and which may if desired be located in a water or other bath 12 warmed by suitable means 13. The top of'the receptacle 11 isconnected by an inverted U-tube 14 with the top of an elongated reservoir 15, the bottom of which is connected by'a U- tube 16 with any suitably shaped reservoir 17. The top of the reservoir 17 is provided with a tube 18, through which a regularly variable pressure may be maintained on a liquid 19 in the reservoir and tube 16. This liquid is the desiccating or drying agent and may conveniently be sulphuric acid. branch 20 leads from the bottom of the res ervoir 15 and is connected at its upper end with one arm 210f a U-tube. The other arm 22 of this tube is provided above the upper end of the branch 20 w'ith an enlargement or receiver 23. The pressure regulating means to which the tube 18 is connected is preferably an apparatus giving alternate sub-atmospheric and atmospheric pressures, such as a Topler mercury Vacuum' tube 16 remains at the level a and airin the remainder of the apparatus is partially evacuated. If now suction ceases through the tube 18 and atmospheric pressure is admitted, the liquid will shift to approximately the levelsb,b. The liquid will which is absorbed by the desiccating also fill the tubes 20, 2]. and 22 and partly fill the receiver 23. When suction is again exerted through the tube 18, the liquid tends to resume the levels a. The suction through the tube 22, however, retains liquid. therein and while a certain amount is withdrawn by the counter suction, enough remain to form a seal in the iii-tube, as indicated by the levels (Z. As the liquid tends to resume its level 0;, it naturally recedes from the tube 20, so that a perfect vacuum is created in this tube. When the liquid drops below the entrance of the tube 20, to approximately the levels 0, the atmosphere above the liquid level equalizes with the vacuum. The 'means 24 in the reservoir is now left uncovered and wetted with the desiccating agent, so that a large absorption surface is presented, with the result that a great part of the vapor in the atmosphere is absorbed. When atmospheric pressure is readmitted through the tube 18, the liquid rushes up to its levels Z; and as soon as it rises above the mouth of the tube 20, air therein is trapped. Continued rise of the liquid in the tube 241) expels the air through the tube 21 and through the liquid in the tube 22 and receiver 23. The operation continues automatically as just described until almost a perfect vacuum has been produced in the receptacle 11, the air removed being expelled and the vapor absorbed by the desiccating agent. Once the air has been removed, the atmosphere in the receiver 15 and receptacle 11 is solely aqueous vapor, agent. This absorption is very rapid, owing to the agent being exposed over the lar e area oi? the means 24 at each oscillation of the liquid.v It is well known that when the pressure on a liquid is lowered, its boiling or evaporation point is correspondingly lowered. It is also welllrnown that in the physical change f known as evaporation a large amount of heat is absorbed. l/Vith the low pressures and consequent extremely rapid evaporation in the present apparatus very low temperatures will be produced. It will therefore be necessary in many instances to provide sutli cient heat to prevent freezing of the mate rial dried, especially when this material is readily freezable liquid. In such cases, any

suitable heating apparatus 13 is utilized;

the flame and temperature equalizing bath shown in the diagram being purely for purpose of illustration. By meansot this ap paratus, liquids in the receptacle 11 may be vigorously boiled at a temperature of 10 0., with the result that the discharge of water or other vapor will be very rapid.

An advantage of this invention is that the pressure in the apparatus is reduced to the vapor pressure of the desiccating agent, so that absorption of the extracted vapor is facilitated. As an example of the results produced by this method, it may be stated that at ordinary temperature, a month is required for a liter of Water to be evaporated and absorbed in a liter of sulphuric acid, whereas according to this process, a liter of water at the same temperature may be evaporated and completely absorbed by liter of sulphuric acid in approximately two and one-halt hours. This invention presents further advantages, for example, when exhausting air to promote evaporation with a Topler mercury pump or a rotary pump, the suction apparatus soon becomes saturated with water films, after which there is great loss of efiiciency, owing to the fact that the pressure is reduced only to that of water at the temperature at which the pump is operated. According to this invention, the water is absorbed and held by the suction apparatus and does not interfere with its operation. The air is automatically discharged at each operation of the liquid. A further great advantage of this invention is that it eliminates the last few millimeters pressure of air or inert gas in the apparatus, producing substantially a perqtect vacuum. It has been of course known for a very long time that liquids evaporate more rapidly at low pressures, but it was thought that the last few millimeters of air or inert gas pressure in an evaporating apparatus did not effect evaporation and the maximum rate of evaporation had been obtained. I have discovered by experiment that the rate of evaporation is by no means proportional to the pressure and that if the last two or three millimeters of air or gas pressure can be removed, the rate of evaporation is very greatly increased. According to this process, the air or inert gas pressure in the ap paratus is reduced substantially to zero and it is largely owing to this that the high rate of evaporation is contained. It will be understood that while. the pressure of air or inert gas has been reduced to zero, there will nevertheless be the vapor pressure of the liquid evaporated in the apparatus. It must therefore be understood that the expression vacuum, as used in this specification, is to be considered only as referring to the air or inert gas.

A considerable dificulty is experienced in preparing pure and uniform commercial solutions of sulphuric acid. According to this process, the acid solutions may be quickly and cheaply prepared by evaporating water. WVhen other substances are being dried, of aqueous moisture, the dilute acid is auto matically formed and the sale of this byproduct will largely or wholly ofi'set the cost of the drying operation.

Having thus described my invention, what I claim is 1. A process of drying, consisting in causing the vapors evolved from the material to be dried to contact with a desiccating sur face, periodically wetting the surface with a vapor absorbing agent, by causing the agent to rise and fall over the desiccating surface, the fall of the agent creating a vacuum to expedite the rarefication of the vapors under treatment. i

2. A process of drying consisting in cansing the vapors evolved from the material to be dried to contact with an extensive desiccating surface, alternately raising and lowering the level of a desiccating liquid to periodically wet such surface, the movement ofthe liquid effecting a vacuum to assist in the rarefication of the atmosphere under treatment.

3. A process of drying consisting in causing the vapors evolved from the material to be dried to pass in contact with an extensive desiccating surface, periodically raising and lowering the level of a desiccating liquid to wet such surface, the receding action of the agent creating a vacuum which in conjunction with the desiccating agent efiects rarefication of the atmosphere under 'treatment.

4. A process of drying, comprising distribution of a desiccating agent over a distributing surface, periodically renewing such distributed agent by causing the desiccating agent to rise and fall over the said surface,

this movement of the agent simultaneously evacuating air from the vicinity of the material to be dried.

5. A process of drying comprising placing vacuum in such vessel, and heating the material tobe dried sufliciently to prevent freez- 5 ing by the accelerated evaporation.

6. A process according to claim 5 in which the heating is carried out at a temperature sufficient to boil the liquid treated at the re-- duced pressure.

7. A method for making dilute sulphuric acid which comprises placing water in a closed receptacle, communicating with a. chamber having an extensive desiccating surface alternately raising and lowering the level of a column .of sulphuric acid to Peri-- odically distribute such acid over said surface and to create a vacuum and heating the water to accelerate evaporation.

In wltness whereof, I have hereunto set my hand.

OTTO MAASS.- 

